Effective communication on paper is not the same as communicating through speech. Written communication follows different rules of logic, layout, conciseness and clarity which is not expected in speech. Learn these structures and format, and anyone can write clearly and effectively.

Good writing and critical thinking work together

Writing is not separate from thinking: we cannot think through really complex problems and solve them mentally. We certainly cannot communicate to others our mental understandings of solutions unless we use sequential words. If you want a critically sophisticated argument/thesis, then you need to learn how to draft and edit your work.

A thesis is not your results; it is a whole story

We need to think about what the reader needs to know, not just think about describing the results. Good writers learn to stand back from their work and see it as others need to see it. They tell the whole story and not just one aspect...